1. Field of Invention
The present invention relates to valve spring and valve stem seal assemblies for use in internal combustion engines, and more particularly to bottom flange portions of such assemblies adapted to bear against cylinder head decks.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves include integral elongated stems extending away from the engine cylinder heads, the ends of the stems interacting with rotating cams for cyclic repeated opening and closure of the valves during the combustion cycle.
The valve stems thus move reciprocally to and from the cylinder head, and so-called valve stem seal assemblies, also variously called valve seal assemblies, are used to seal against leakage of oil through a clearance path between each annular engine valve guide and an associated valve stem supported for reciprocal motion within that particular guide. Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem.
Thus as is well known, the intake ports of a combustion chamber are opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotary with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of the same construction, and include stems integrally affixed to the valves.
In the typical engine, a valve seal assembly is fitted over each valve stem, each assembly being frictionally mounted over an associated valve guide to assure its securement within the engine. The valve guide normally extends upwardly from a cylinder head deck of the engine. Typically each valve seal assembly has two primary parts; 1) an elastomeric valve seal positioned at its upper end to control leakage of oil between the valve stem and guide as noted, and 2) a structural cylindrical part called a retainer which is mounted atop of, and is axially secured to, the valve guide.
In some cases, the retainer has a so-called bottom flange that extends radially over and against the valve spring seat of the cylinder head deck. As those skilled in the art will appreciate, the cylinder head deck provides support for the bottom flange, or so-called spring seat flange, against which valve return springs bear. One recurring issue has been that the bottom of the spring seat flange tends to rotate under conditions of vibration, producing undesirable wear between the cylinder head deck and the flange.
In some limited cases, particularly relating to exhaust valves, no valve stem seal assembly is included. Under the latter arrangement, only a guide and stem is employed, and the valve return spring typically bears against a washer instead of a seal retainer flange. In such cases, the washer gives rise to the same problem.
Several techniques and structures for preventing rotation of valve stem seal parts that bear against a valve spring and/or a cylinder head deck have been proffered, including tabs designed to avoid rotation of valve stem seal parts for avoidance of wear. However, there has not yet been a fully satisfactory solution to the issue presented.